It is an illegal advertising application that secretly works in background and shows undesirable commercial information. 12Trojan.Win32.Krepper.ab shows advertisements in numerous pop-ups, web browser windows or toolbars. It can get into the computer from unsafe web sites. Some ad-supported softwares include it as a component. 12Trojan.Win32.Krepper.ab doesn't possess any serious threat to the computer security, but may severely violate user privacy.